This invention relates to bit addressable linear modulators and, more particularly, to method and apparatus for avoiding destructive interference between upper and lower sidebands of the modulator output beam.
Bit addressable linear modulators may be utilized with an electro-optic line printer as a means for converting image signals or pixels, representing the original image, to an image copy. A modulator of this type is disclosed in U.S. Pat. No. 4,281,904 and issued to R. A. Sprague et al on Aug. 4, 1981 for a "TIR Electro-Optic Modulator With Individually Addressed Electrodes".
In the aforementioned electro-optic printer, a photosensitive recording medium, such as xerographic photoreceptor, is exposed in an image configuration as the recording medium is advanced along an axis perpendicular to the direction of scan. For scanning purposes, a sheet-like collimated light beam derived from a suitable source such as a laser, is transmitted through the electro-optic modulator, such transmission being either along the modulator's optical axis for straight through transmission or at a slight angle relative to the modulator axis for total internal reflection. Concurrently therewith, image signals or pixels, which may be in the form of digital bits or analog signals are sequentially applied to the modulator electrodes. As a result, localized electric bulk or fringe fields are created within the electro-optic element in the immediate vicinity of any electrodes to which non-reference image signals are applied. Where such fields occur, localized variations in the refractive index of the modulator substrate take place and these variations in the refractive index of the substrate in turn modulate the phase front or polarization of the light beam passing therethrough in accordance with the image signal content. The phase front modulated light beam is thereafter converted into a light beam having a correspondingly modulated intensity profile which is impinged onto the recording medium to create an image representative of the image signals. The image so created is thereafter processed xerographically to provide a visible rendition or copy of the original image.